The purpose of this research is to gain further insight into the molecular mechanisms that are involved with blood vessel formation. Blood vessel formation is not only critical for normal development, but plays an essential role in the pathogenesis of many diseases. The molecular basis of this complex process has been meticulously characterized over the past few decades. Angiogenesis and vasculogenesis are both essential components of blood vessel formation. These processes require elaborate interactions between cell adhesion molecules, growth factors, extracellular matrix proteins, and intracellular signaling pathways. Adhesion molecules have been found to play a pivotal role in morphogenesis, organogenesis, and vasculogenesis. Recently, a novel immunoglobulin-type adhesion molecule named endothelial cell-specific adhesion molecule (ESAM) was cloned. ESAM expression is localized to endothelial cells and may play a fundamental role in endothelial cell development. Studies are proposed to characterize the role of ESAM in blood vessel formation. To evaluate the in vivo role of this molecule, mice lacking functional ESAM will be produced. In vitro and animal studies will be performed to determine whether ESAM plays a role in angiogenesis.